1. Technical Field
The present invention relates to a photographing optical lens system. More particularly, the present invention relates to a compact photographing optical lens system applicable to electronic products.
2. Description of Related Art
In recent years, with the popularity of mobile products with camera functionalities, the demand for miniaturizing an image lens system is increasing. The sensor of a conventional photographing camera is typically a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor. As advanced semiconductor manufacturing technologies have allowed the pixel size of sensors to be reduced and compact image lens system has gradually evolved toward the field of higher megapixels, there is an increasing demand for compact image lens system featuring better image quality.
A conventional compact image lens assembly employed in a portable electronic product mainly adopts a four lens elements structure. Due to the popularity of mobile products with high specification, such as smart phones and PDAs (Personal Digital Assistants), the pixel and image quality requirements of the compact image lens assembly have increased rapidly. However, the conventional four lens elements structure cannot satisfy the requirements of the compact image lens assembly.
Another conventional compact image lens assembly provides a five lens elements structure, wherein lens elements are the first through fifth lens elements in order from an object side to an image side. The image lens assembly with five lens elements can increase the image quality and resolving power thereof. However, only one of the fourth lens element and the fifth lens element has negative refractive power, so that the negative refractive power of the image lens assembly cannot be properly distributed and the sensitivity thereof cannot be reduced. Moreover, the principal point of the image lens assembly cannot be positioned away from the image plane for reducing the back focal length thereof due to the surface shape of the fourth lens element and the fifth lens element.